1. Field of the Invention
The present disclosure relates to a passive safety facility to enhance cooling performance and to reduce radioactive materials within the containment during an accident by introducing a fluid circulation increasing device and filter facility, and a nuclear power plant including the same.
2. Description of the Related Art
Reactor is divided into a loop type reactor and an integrated type reactor according to the installation location of main components. When the main components (a steam generator, a pressurizer, a pump, etc.) are installed outside a reactor vessel, it is classified as a loop type reactor (for example, commercial reactor: Korea). When the main components are installed within a reactor vessel, however, it is classified as an integrated type reactor (for example, SMART reactor: Korea).
Furthermore, reactor is divided into an active type reactor and a passive type reactor according to the implementation method of a safety system. The active type reactor uses an active component such as a pump operated by electric power from an emergency diesel generator or the like to drive the safety system. On the other hand, the passive type reactor uses a passive component operated by passive power such as gravity, gas pressure or the like to drive the safety system. When an accident occurs in the passive type reactor, the passive safety system maintains the reactor in a safe condition for at least a period of time (72 hours) according to the regulatory requirements by using only natural forces integrated in the system even without any operator actions or alternating current (AC) power of a safety class such as an emergency diesel. The operator action or non-safety system involvement is allowable in the passive safety system operation after 72 hours following the design basis accidents.
In the related art, a passive residual heat removal system and a passive containment cooling system have been configured using a steel containment and a secondary side of a steam generator (Korean Patent Publication No. 10-2013-0047871). However, it is preferable to adopt the reinforced concrete-type containment building rather than the steel containment applied to the related art due to difficulties in manufacturing and maintenance, low economic efficiency, and the like. Hereinafter, a passive residual heat removal system and a passive containment cooling system will be described, respectively.
The passive residual heat removal system is employed to remove heat in a reactor coolant system (sensible heat in the reactor coolant system and residual heat in the core) during an accident in various reactors including the integrated type reactor. For a cooling water circulation method of the passive residual heat removal system, two types are mainly used, such as a primary fluid circulating method to cool the reactor coolant system (AP1000: United States Westinghouse Company) and a secondary fluid circulating method using a steam generator to cool the reactor coolant system (SMART reactor: Korea), and a method of injecting primary fluid to a condensation tank to directly condensate it (CAREM: Argentina) is also partly used.
Furthermore, for a cooling method of the heat exchanger (condensation heat exchanger) in the passive residual heat removal system, a water-cooled type (AP1000) that is used most frequently, an air-cooled type (WWER 1000: Russia), and a water-air hybrid cooled type (IMR: Japan) are used. The heat exchanger in the passive residual heat removal system transfers heat received from the reactor coolant system to an outside (ultimate heat sink) through an emergency cooling water storage section or the like. For a method of heat exchanger, a condensation heat exchanger with high heat transfer efficiency using steam condensation phenomenon is mainly used.
The passive containment cooling system is one of several safety systems for reducing pressure, temperature, and a concentration of radioactive materials. The passive containment cooling system is employed to suppress the increase of pressure and to remove the heat within the containment (reactor building, containment or safeguard vessel) during an accident in various nuclear reactors including the integrated type reactor. For a configuration method of the function of the passive containment cooling system, a method of using a suppression tank for condensing the steam discharged to the containment building (Commercial BWR, CAREM: Argentina, IRIS: United States Westinghouse Company, etc.), a method of applying a steel containment and cooling an outer wall (water spray, air cooling) (AP1000: United States Westinghouse Company), and a method of using a heat exchanger (SWR1000: France Framatome ANP, AHWR: India, SBWR: United States GE), and the like are used.
As described above, in general, the passive residual heat removal system using the secondary side of the steam generator mainly uses a method of installing a heat sink (emergency cooling water storage section) outside the containment using a natural circulation. The cooling water that is cooled within the condensation heat exchanger is supplied to the steam generator by gravitational force, and the steam that is formed within the steam generator while removing the heat of the reactor coolant system is circulated to the condensation heat exchanger continuously (Korean Patent Publication No. 10-2013-0047871).
On the other hand, the passive containment cooling system generally uses a method of removing heat within the containment by natural circulation flow formed within the containment without any other flow inducing means. Furthermore, the passive residual heat removal system and passive containment cooling system are typically designed independently.
The performance of the passive containment cooling system in the related art has been determined only by natural circulation flow without any additional devices for forming the flow thereof.
In such a configuration where natural convection is dominant, the heat transfer coefficient on a surface over which the atmosphere (air and steam) flows is very small, thereby causing a problem in which the size of the heat exchanger should be greatly increased. Meanwhile, the heat exchanger may be a structure of forming a pressure boundary of the containment, thus a possibility of the pressure boundary break may increase when the size of the heat exchanger increases, thereby causing a problem of decreasing the safety.